A flight path of an airplane is controlled by a deflection of flight control surfaces. In many modern airplanes, flight control surfaces are deflected by actuator(s). Such flight control surfaces may include elevators for pitch control, ailerons and flaperons for roll control, and a rudder for yaw control. In many cases, electric current controls output of the actuator. In some cases, an electromagnetic effect of the electric current directly produces a mechanical output for Electro-Mechanical Actuator (EMA), or Electro-Hydrostatic Actuator (EHA), while in other cases, it is amplified by some other means, such as through controlling the hydraulic flow through a servo valve such as a Direct-Drive Valve (DDV), or Electrohydraulic Servo Valve (EHSV) in single or multiple stages.
Electric current flows through a coil (or coils) and is converted to a magnetically induced useable force to actuate the actuator. A non-optimality causing an erroneous level of current could cause the actuator to move to an un-commanded position or output an un-commanded force. Such a non-optimality may cause an airplane to deviate from a commanded path and/or cause structural anomaly to the airplane, particularly if the non-optimality is oscillatory or cyclic.